飞秒激光光刻波导偏振器

Femtosecond Laser Photoinscription of Waveguide Polarizer

飞秒激光诱导折射率变化提供了一种灵活的三维光子器件制作手段.飞秒激光光刻的II类波导具有偏振导光特性,可以作为波导偏振器,但是对于要保留的偏振分量损耗太大.本文阐述了一种利用飞秒激光在熔融石英中制作的新型低损耗波导偏振器.它由中间的一根I类波导及两侧的两根II类纳米光栅轨迹构成.基于飞秒激光诱导的纳米光栅的偏振依赖散射特性,II类纳米光栅轨迹能够对I类波导的倏逝场进行调制.偏振方向垂直于纳米光栅的模式相对于偏振方向平行于纳米光栅的模式有更大的散射损耗,因此导通的是偏振方向平行于纳米光栅的模式.研究了消光比随I类波导与II类纳米光栅轨迹之间的间距的变化关系,选择一个最佳间距来进一步研究消光比随II类纳米光栅轨迹长度的变化关系.在间距6μm,II类纳米光栅轨迹扫描长度6 mm处实现了最大15.91 dB的消光比.通过增加II类轨迹的长度或者数量,很容易得到更高的消光比.

Femtosecond laser inducing refractive index modification has provided a flexible avenue to three-dimensional photonic devices.Having polarization dependent guiding properties,femtosecond photowritten type II waveguide can be used as waveguide polarizer,but it experiences high loss for reserved polarization component.A new type of low loss waveguide polarizer fabricated in fused silica using femtosecond laser was reported.It consists of a type I waveguide in the middle and two type II nanograting traces on both sides.Based on the polarization dependent scattering properties of nanograting indued by femtosecond laser,the evanescent field of type I waveguide was modulated by the type II nanograting traces.Because the mode having a polarization perpendicular to the nanograting experiences a higher scattering loss compared with the mode having a polarization parellel to the nanograting,the latter was transmitted more efficiently.Firstly,polarization extinction ratio as a function of the separation between type I waveguide and type II nanograting trace was investigated.Using the best separation,polarization extinction ratio as a function of the length of type II nanograting trace was further investigated.Extinction ratio up to 15.91 dB between orthogonal polarizations have been realized with a separation of 6 μm and a type II nanograting trace length of 6 mm.Higher extinction ratio could be easily realized by increasing the length of type II nanograting traces or the amount of type II nanograting traces.